sass/dart-sass

Use worker threads to implement render()

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#868 opened on Oct 30, 2019

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 (7 comments) (8 reactions) (0 assignees)Dart (4,192 stars) (376 forks)batch import
JavaScriptenhancementhelp wanted

Description

Currently, we implement the asynchronous render() method in Node.js in one of two ways:

  • By default, it's run through the AsyncEvaluator which is synchronized via code gen with the synchronous Evaluator. This is much slower than running synchronously, and imposes developer overhead by requiring synchronization.

  • If the user passes in a reference to the fibers package (which uses a C++ extension to add a coroutine-style asynchrony model to Node), we run the synchronous code path and use coroutines to call out to async helpers. This is as fast as running synchronously but requires the end user to opt in to a C++ compilation which may be difficult to compile.

Sass's business logic itself is fully synchronous, so we get no benefit from this asynchrony other than the ability to invoke asynchronous function and importer callbacks. I think we can avoid the downsides of both of these methods by running the whole Sass compiler in a worker thread and using Atomics.wait() to block that thread until the callback completes.

Contributor guide

Tech stack
nodejs
Domain
backendperformance
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Node.js async patternsworker threads moduleSass render pipelineAtomics.wait
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20
Research direction
Examine the current AsyncEvaluator implementation and the synchronous Evaluator in the Node.js entry point (likely `lib/src/async evaluator.dart` and `lib/src/evaluator.dart`). Understand how the fibers package was used as an alternative. Research the worker threads API and Atomics.wait for blocking. Review comments in the issue for any prior attempts or concerns. Start by prototyping a minimal worker thread wrapper around the synchronous render path.